Blacks have higher testosterone levels and therefore are more promiscuous, rape more, have bigger penises and so on...
Obviously more frequent less constraint sexual activity coupled with drug use leads to increased aids level.

Actually, black people gets AIDS more than white people because the parts of Africa (Congo, specifically) where AIDS developed are nearly universally occupied by local black people. And then they were easily spread to other black people in ajoining countries- who were weakened by the other diseases like Malaria, Typhoid, Diarrhea and sleeping sickness, all of which kill more people than AIDS BTW- who spread it along roads via truckies, and then into countries via armies. And then they started using it as a weapon.

And these African nations, remember, have no money. They are incapable of obtaining even basic medicine for easily and cheaply curable diseases, let alone the really expensive stuff for AIDS.